The present invention relates to a prespray processed cylinder inside and a cylinder inside prespray processing method for preparing the surface of a cylinder inside to be roughed for a spray film to be formed thereon.
As a preliminary process for formation of a spray film to a cylinder inside or bore of a liner-less aluminum cylinder block that is advantageous for weight reduction and exhaust processing of an automobile engine, a roughing to the cylinder inside is needed to achieve an enhanced adhesion of the spray film. There is disclosed a blasting as a roughing method in Japanese Patent Application Laying-Open Publication No. 11-320414.
The blasting employs an abrasive material, which is abrasive in repeated use, causing the surface condition of blasted cylinder inside to be varied, resulting in a bad subsequent influence on the adhesion strength of spray film.
A blast gun is vertically moved and rotated for the blasting, needing a masking material for preventing a collision of abrasive material to a crankshaft bearing surface or a mating surface of the cylinder head, resulting in an enlarged scale and complexity of an entire installation.
The abrasive material and masking material are consumed, accompanying scattered powder dust, with a bad influence on the working environment, and those consumables in use causes an increased cost and replacement work, leading to a reduced productivity.
It is an object of the present invention to form a rough surface allowing for a spray film on a cylinder inside to have an enhanced adhesion strength, possibly avoiding accompanying an enlarged scale or complexity of an entire installation nor leading to a bad working environment or reduced productivity.
To achieve the object, according to an aspect of the present invention, there is provided a prespray processed cylinder inside comprising a cylindrical surface prepared for a spray film to be formed thereon and roughed with a set of first undulations cut therein in a threaded form, including a subset thereof having ridge parts of first undulations thereof broken and formed with a set of second undulations finer in undulation width than a first undulation.
According to another aspect of the present invention, there is provided a cylinder inside prespray processing method comprising preparing a cylindrical surface for a spray film to be formed thereon, roughing the cylindrical surface by cutting therein a set of first undulations in a threaded form, having ridge parts of first undulations of a subset thereof broken and formed with a set of second undulations finer in undulation width than a first undulation.
According to these aspects of the invention, a cylindrical surface has a set of first undulations cut therein in a threaded form, of which a subset has first undulations thereof, which have their ridge parts (that may be original surface parts left between cut grooves), which ridge parts are broken and have their broken surfaces, of which an entirety is defined by a set of second undulations, so that a respective broken surface at the ridge part of a corresponding first undulation is defined by a corresponding subset of the set of second undulations. Any second undulation in the corresponding subset of second undulations is finer in undulation width than the corresponding first undulation.
Accordingly, the cut cylindrical surface, which is configured in a threaded form with first undulations that have their groove parts and their ridge parts with broken surfaces defined by fine second undulations, allows a spray film to intrude into the groove parts and onto the broken surfaces, resulting in an enhanced adhesion strength, in particular, at the fine second undulations.
It is noted that, when cutting a surface by a cutting tool, the way or direction for cut chips to leave can be set. The ridge part of a first undulation may preferably be broken or torn by a cut chip leaving a cut groove part of the first undulation, in a preset direction or in a preset cut form. In this case, the blasting process may not be used for roughing a cylinder inside, successfully avoiding accompanying an enlarged scale or complexity of an entire installation nor leading to a bad working environment or reduced productivity.
In this respect, according to another aspect of the present invention, the cutting includes having a cut chip leaving a groove part of an arbitrary first undulation in a preset direction, breaking a ridge part of the arbitrary first undulation to form therein a subset of the set of second undulations.
Furthermore, according to another aspect of the present invention, the cutting includes feeding a cutting tool in an axial direction of the cylindrical surface, rotating the cutting tool to cut the set of first undulations in the cylindrical surface, having the ridge parts broken and formed with the set of second undulations.
Still more, according to another aspect of the present invention, the cutting includes cutting a groove part of an arbitrary first undulation, uncutting a top portion of a ridge part of an associated first undulation, and having a cut chip leaving the groove part, tearing off and carrying together the top portion of the ridge part, having a subset of the set of second undulations formed in a remainder of the ridge part.
Yet more, according to another aspect of the present invention, the cutting includes cutting a groove part and one side of a ridge part of an arbitrary first undulation, uncutting a top portion of the ridge part to have a cut chip integral with the top portion, making the cut chip leave the groove part, tearing off the top portion from a remainder of the ridge part, having a subset of the set of second undulations formed in the remainder.